I omitted the 350 and 650 initially because I don't think they are good candidates for starting points.
The 650 lacks a kickstarter and is starting to move more toward the lo-slung "American" style of bike with it's aesthetics. Gonna spend more to get it the way you want.
The 400 is a modified 350 and if you take the 350 all the way to town, you are covering ground that Honda already covered in the 400, so the 400 makes a better starting point than the 350.
The only ones I would consider, FOR ME, are the 550, 750 and 400, but I included the 500 because the better 550 engine ad gearbox can be dropped right into the 500 frame. Though I guess you could drop the 400 motor right into the 350 frame.